Any GPS loggers?

I'm working on a custom mapping/routing program that works similar to streets & trips, mapquest, etc, but uses real traffic information to give accurate routes and times. One of the key pieces of information is how people are driving and the speeds they drive on roads. I currently log all my trips to a text file, storing the time and lat/long.

Is anyone else doing this, and are you willing to give up your data files? Doesn't matter what format it is in, as long as it has lat & long and time. I REALLY need data from the DC metro area, specifically Fairfax & Arlington Counties, Virginia. That way i can tie my data in w/ yours. If you live in this area and use GPS, and are willing to... please log your trips!